1. Field of the Invention
The present invention relates to a ball array mask and a ball array mask supporting apparatus. The present invention has been developed with mainly focus on a ball array mask and a ball array mask supporting apparatus utilized for a system that arrays minute balls by relatively moving a ball cup storing the minute balls over an array mask having through holes by way of which the balls are inserted into a predetermined pattern.
2. Description of the Related Art
In a solder ball mounting apparatus that mounts solder balls on respective electrodes formed on a wafer, which is an object to be mounted, in a predetermined array pattern, the number of solder balls to be mounted by one operation is increased as a result of miniaturization of the solder balls and an increase in the size of a product which is an object to be mounted, such as a wafer. Under such a circumstance, in order to diminish occurrence of defects in the array of solder balls or defects, which would otherwise be caused during mounting, there has been provided a related art solder ball mounting apparatus that mounts a ball array mask over a wafer printed with flux, wherein a ball cup moves over the ball array mask and drops solder balls directly on electrodes of a wafer.
As for such a related art solder ball mounting apparatus, JP-A-2007-324404 discloses a technique, in which a base member is arranged so as to surround an object to be mounted, a ball array mask is brought and held into contact with and on an upper edge of the base member (a backup plate) under tensile force, thereby enhancing plane accuracy of the ball array mask. A tensile force imparting unit employed in the related art solder ball mounting apparatus is embodied by attaching holding block members to respective corners of the metal mask and stretching the holding block members outside.
However, the tensile force imparting unit pulls the corners of the metal mask. When the metal mask is square, obliquely outward tensile force is exerted on the metal mask, and sufficient tensile force, is exerted around the respective corners. However, there has also arisen a case where insufficient tensile force is imparted to center portions of respective sides of the metal mask. Since the metal mask is made of metal, such as very thin nickel, there is a risk of the metal mask being crimped in some way of holding at the time of operation for attaching and detaching the metal mask to and from the ball array mask supporting apparatus or a potential risk of a finger being cut by a sharp edge of the metal mask. Thus, the metal mask is difficult to handle.